DESCRIPTION: None of the established therapies for patients with Pulmonary Arterial Hypertension (PAH) reduce mortality or reverse established pulmonary vasculopathy. However, patients with Hereditary PAH (HPAH) inherit heterozygous, autosomal dominant mutations in the BMP type 2 receptor gene, BMPR2, suggesting that strategies to correct BMP signaling defects could present a new therapeutic approach for this disease. Over 300 HPAH BMPR2 mutations have been identified, each with potentially different effects on BMPR2 function. However, these can be classified into 3 functional groups: i) Class I: mRNA is degraded by non-sense mediated RNA decay, (NMD+); ii) Class II: receptors are expressed (NMD-), but mis-folded and are not expressed on the cell surface; and iii) Class III: receptors are expressed (NMD-) and correctly localized but non functional. This classification is important since NMD inhibitors may restore BMP signaling with Class I mutations, while compounds that correct protein folding may restore signaling with Class II but not Class III BMPR2 mutations. Importantly, both NMD inhibitors and protein folding agents, are effective, safe and being evaluated in patients with other heritable diseases, such as cystic fibrosis. These studies will determine whether mutation-specific therapies also correct BMPR2 expression and function in HPAH patients. As an initial step to establish the applicability of this paradigm in HPAH, we will use HPAH patient-derived endothelial cells (ECs). Ideally we would use pulmonary endothelial cells (PECs) from HPAH patients for all of these studies. However these cells are in limited supply and have short lifespan in culture. For this reason we will supplement initial studies using HPAH PECs obtained from the PHBI Cell Core, with studies using late outgrowth endothelial progenitor cells (LEPCs) obtained from peripheral blood of HPAH patients with known BMPR2 mutations. Some of these cells have been generated and will be provided by a collaborator. However, we are in a unique position at Vanderbilt to supplement these studies using samples derived from the largest cohort of HPAH patients with defined BMPR2 mutations in the USA. In this way we will be able to study a cohort of HPAH patient-derived ECs that include a representative distribution of BMPR2 mutations from all 3 functional classes of mutation. Using these cells therefore, we will determine the nature and functional classification of BMPR2 mutations, and evaluate the effects of NMD pathway inhibitors and protein folding agents on BMPR2 expression and function in these HPAH patients. These studies therefore will identify BMPR2 mutant sub-types and responsiveness to NMD pathway or protein folding therapy in a relevant cell type, and will form the foundation to classify therapeutically targetable BMPR2 mutations and more extensive evaluation of NMD inhibitors and/or protein folding agents in HPAH.